JPH0267504A - Method for splicing optical fiber by fusion - Google Patents

Abstract

PURPOSE:To prevent deterioration in mechanical strength of the splicing section of a pair of optical fibers to be spliced with each other caused by crystallization at the time of fusion by exposing end sections of the pair of coated optical fibers and fusing the end faces of the fibers by heating and, at the same time, heating a thermoplastic resin so that the resin can flow and cover the entire surface of the splicing section of the fibers. CONSTITUTION:End faces of optical fibers 1 of a fluoride to be connected with each other are prepared by removing the covering material 2 of the fibers 1 from the end sections and the end sections of fibers are cut off from points near the ends of the covering material 2. Then the fibers are clamped and aligned to each other on a V-groove base 4 for positioning by means of clamps 5 which clamp the fibers by the covering material and the end faces of the fibers are pressed against each other while the fibers are heated so that the resin covering the fibers can melt and flow toward the end face joining section. In other words, the entire surface of the optical fiber connecting section is covered with the resin. Therefore, deterioration in mechanical strength of the fusion-splicing section by crystallization can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application] The present invention relates to a fusion splicing method for optical fibers, and particularly to a fusion splicing method suitable for application to fluoride optical fibers.

[Prior Art] When constructing a communication system using optical fibers, optical fiber connections are essential. Fusion splicing is a method for connecting optical fibers. In this connection method, optical fibers are joined by heating and melting, and as a heat source, electric discharge, carbon dioxide laser, gas flame, electric wire heater, etc. can be used.

This connection method has the advantage of superior long-term reliability and connection loss compared to other connection methods that use adhesives.

Fluoride optical fibers are being studied as a future optical communications transmission medium because they have the potential to have lower optical transmission loss than the currently used stone-based optical fibers. If this optical fiber is to be put into practical use, the splice loss must also be lower than that of conventional silica-based optical fibers, and therefore the fusion splicing method is expected to be applied. Since the melting point of this optical fiber is low, it is necessary to lower the heating temperature during fusion splicing (the heating temperature is about 300°C to 400°C, compared to 2000°C for quartz-based fibers).

Possible methods for solving this problem include a method using discharge heating and a method using a carbon dioxide gas laser, and since the feasibility of the connection method has already been experimentally confirmed, it is thought that there are not many obstacles.

It is possible that other heat sources can lower the heating temperature during fusion splicing.

Another problem to be solved is that, from a material standpoint, this fluoride optical fiber tends to crystallize when heated. This crystallization is sensitive to the heating atmosphere, and in particular, crystallization is significantly accelerated by moisture in the air.

In the fusion splicing methods tried so far, the ends of the optical fibers are heated bare until the end of the connection, similar to the method of splicing silica-based optical fibers, so crystallization occurs on the surface of the optical fiber splices. Cheap.

Therefore, unless a special heating atmosphere is created, the only convenient countermeasure is to select and set conditions that minimize crystallization by adjusting the heating time and heating temperature, and prevent the deterioration of mechanical strength due to crystallization. was difficult. In addition, this heating condition with relatively little crystallization does not match the optimal heating condition in terms of splice loss, so it is difficult to form a joint with excellent strength and splice loss. Conceivable. In addition, adopting a method of creating a special heating atmosphere poses practical problems because it increases the cost of the connecting device and is thought to significantly impair the connection workability.

[Problems to be Solved by the Invention] Therefore, the purpose of the present invention is to solve the above-mentioned problems, prevent deterioration of mechanical strength due to crystallization during heating, and provide good connection workability during fusion bonding. An object of the present invention is to provide a fusion splicing method for fluoride optical fibers that can form a spliced portion that is excellent in both strength and splicing loss.

Since the conditions can be freely selected, it is possible to form connections that are excellent in both strength and connection loss.

[Means for Solving the Problem] In order to achieve such an object, the present invention exposes the ends of a pair of opposing optical fibers coated with a thermoplastic resin, and connects the pair of optical fibers to be connected. The end faces of the fibers are faced to each other and their axes are aligned, the end faces of the optical fibers to be connected are pressed together while heating, the end faces of the optical fibers to be connected are fused, and the heated flow of the thermoplastic resin causes the optical fibers to be connected to each other. It is characterized by covering the entire connection part.

[Function] The present invention covers the bare portion of the fluoride optical fiber with molten resin and isolates it from the outside air immediately after starting heating for fusion splicing. It has the effect of preventing strength deterioration.

Therefore, since there are no restrictions on the setting of the heating time and heating temperature, in order to reduce the connection loss [Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a top view showing the steps of a fusion splicing method according to an embodiment of the present invention. In FIG. 1, 1 is a fluoride optical fiber, 2 is a coating, 3 is a heating area, 4 is a V-mount for positioning,
5 is a clamp. The coating 2 described above is stripped from the end of the optical fiber, and the optical fiber is cut near the end of the remaining coating to form an end face. Here, the fluoride optical fiber needs to be coated (at least at its end) with a thermoplastic resin. This resin melts below the heating temperature during fusion, and does not undergo deterioration even after heating for a few seconds.
Good wettability with the fluoride optical fiber surface is required. An example of a resin that meets this condition is Teflon resin, which is actually used as a coating material for fluoride optical fibers.

The explanation will be given below based on each figure in FIG.

In Figure 1 CB) or D), ■Gandle 4, Clamp 5
has been omitted for brevity.

FIG. 1(A) is a diagram showing a state in which a fluoride optical fiber is set in a connecting device. In this figure, a fluoride optical fiber coating 2 is attached to a V-mount 4 for positioning with a clamp 5. Thereafter, the axes of both fluoride optical fibers 1 are adjusted to match. This operation may be performed in a conventional manner. For example, a method may be used in which the optical power transmitted through the connection portion is monitored, or a method in which the core of the fluoride optical fiber is directly observed from the side. In addition, if the splice loss tolerance is large, the axis adjustment work can be omitted by precisely machining the axes of the left and right V gantry 4 in advance, as is conventionally done with multimode optical fibers. You can also do that.

Next, the end face of the fluoride optical fiber is pressed while heating the fluoride optical fiber. FIG. 1(B) shows a state in which the end faces of the optical fibers have begun to be joined. At this time, the resin coating the optical fiber melts and flows toward the end surface joint of the fluoride optical fiber. This flow phenomenon occurs due to the good wettability of the resin.

FIG. 1(C) shows a state in which the entire surface of the optical fiber connection portion is covered by the flow of the resin. When we conducted a connection experiment using a Teflon-coated fluoride optical fiber and using electrical discharge as a heat source, this state was achieved in less than 1 second after the start of heating. After this state is reached, even if heating continues, the surface of the optical fiber is shielded from the outside air, so crystallization is suppressed.

FIG. 1(D) shows the final state of the connection.

Note that since the coating must be applied after the optical fiber end faces are fused, a time delay is required for the coating resin to cover the entire optical fiber surface so that the coating resin does not flow between the optical fiber end faces before that. It is. Additionally, this coating action can be adjusted to occur immediately after the optical fiber reaches its melting temperature, so that crystallization during this time delay can be sufficiently reduced. This time delay can be adjusted by changing the amount of protrusion of the end face of the optical fiber from the coated end (the length of the bare portion of the optical fiber).

Further, when starting heating, instead of heating the end faces from a separated state, the end faces of the optical fibers may be brought into contact with each other in advance, and the end faces may be pressed together when heating starts. In that case, the part of the optical fiber at the end face is always fused first, so even if the resin gets in between the end faces, it immediately escapes to the outside during pressure welding, so the bare part of the optical fiber as mentioned above The length of may be extremely small. Therefore, the following method can be used for the terminal processing of the optical fiber. That is, in this method, a blade is applied directly to the coated part in the circumferential direction to cut the coat, and the optical fiber is also damaged, and then tension is applied to cut it. In this method, slippage occurs between the optical fiber and the coating when tension is applied, so that it can be used in the connection method of the present invention.

If the coating resin on the end fiber is not suitable for the present invention, remove the coating from the end of the optical fiber, and then cover the bare fiber with a resin tube passed through it, or apply molten resin. The present invention can be carried out by creating a situation equivalent to coating the optical fiber by applying a method of applying the coating material, and by bringing the end of the coating material close to the end face of the optical fiber.

[Effects of the Invention] As explained above, the present invention covers the bare portion of the fluoride optical fiber with molten resin to isolate it from the outside air immediately after starting heating for fusion splicing. It has the effect of preventing strength deterioration due to crystallization of the bonded portion. Therefore, since there are no restrictions on the setting of the heating time and heating temperature, conditions for reducing the connection loss can be freely selected, making it possible to form a connection portion that is excellent in both strength and connection loss.

Furthermore, the present invention greatly contributes to the practical use of communication systems and measurement systems using fluoride optical fibers.

[Brief explanation of the drawing]

FIGS. 1(A) to 1(D) are top views showing the connection process of the embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Optical fiber, 2... Coating, 3... Heating area, 4... V gantry, 5... Clamp.

Claims (1)

[Claims] 1) Expose the ends of a pair of opposing optical fibers to be connected covered with a thermoplastic resin, align the axes of the optical fibers with each other with the end surfaces of the optical fibers facing each other, and Fusion of optical fibers, characterized in that the end faces of the optical fibers are pressed together while being heated, the end faces of the optical fibers to be connected are fused, and the entire connecting portion of the optical fibers to be connected is covered by heating and flow of the thermoplastic resin. Connection method.